Quiz: Java Collections (List and Set)

5 questionsNo time limitPass: 60%+10 XP on first pass

The Collections family as a picture. ArrayList vs LinkedList, HashSet vs TreeSet, generics, iterating safely, and choosing the right collection.

Free account · see your score, answers and explanations, earn XP

Question 1

What does this print?

import java.util.*;
public class Main {
    public static void main(String[] args) {
        Set<String> s = new HashSet<>(List.of("a", "b"));
        s.add("a");
        s.add("c");
        System.out.println(s.size());
    }
}

432Error

Question 2
Which collection keeps elements SORTED automatically?
HashSetArrayListTreeSetLinkedHashSet
Question 3
What is the time complexity of get(i) on an ArrayList?
O(1)O(n)O(log n)O(n²)

Question 4

What does this print?

import java.util.*;
public class Main {
    public static void main(String[] args) {
        List<Integer> l = new ArrayList<>(List.of(10, 20, 30));
        l.remove(1);
        System.out.println(l);
    }
}

[20, 30][10, 30][10, 20, 30][10, 20]

Question 5
What happens if you remove items from an ArrayList inside a for-each loop over it?
It works fineConcurrentModificationExceptionThe list becomes emptyCompile error